PRACTICAL 4
TOPIC : REACTION OF HALOGENS WITH WATER AND
SODIUM HYDROXIDE
NAME: NUR ARIFAH BT MOHD SABRI
MATRIX NO: DPM0010_2013B
PROGRAMME: DIPLOMA IN PHARMACY BATCH APRIL
2013
SEMESTER : 1
DATE : 12 JUNE 2013
OBJECTIVE : To determine the reaction of halogens with water and sodium hydroxide. INTRODUCTION :
The Halogens are typical non–metals and form the 7th Group in the Periodic Table . 'Halogens' means 'salt formers' and the most common compound is sodium chloride which is found from natural
evaporation as huge deposits of 'rock salt' or the even more abundant 'sea salt' in the seas and oceans. The halogen dissociates in water to form it is respective acid or acids. In sodium hydroxide, since all halogens are above hydroxides in the electronegative series, they displace the hydroxide to form the sodiumhalide.
MATERIALS AND APPARATUS :
1. Liquid bromine
2. Liquid chlorine
3. Iodine crystals
4. Distilled water
5. pH paper
6. Dilute sodium hydroxide (0.1M)
8. Dropper
9. Test tube rack
PROCEDURE :
Part A – reaction of halogens with water
I.) With chlorine
1. 5ml of distilled water is poured into a clean test tube. A few drops of liquid chlorine are added into this test tube.
2. The solution is then tested with pH paper. All observations are recorded.
II.) With bromine
1. 5ml of distilled water is poured into a clean test tube. A few drops of liquid bromine are added into this test tube.
2. The solution is then tested with pH paper. All observations are recorded.
III.) With iodine
1. 5ml of distilled water is poured into a clean test tube. A small iodine crystal is added into this test tube.
2. The test tube is then closed with a stopper and shaken well.
Part B – reaction of halogens with sodium hydroxide
I.) Chlorine and sodium hydroxide
1. 5ml of dilute sodium hydroxide is poured into a clean test tube. A few drops of liquid chlorine are added into this test tube.
2. The test tube is then closed with a stopper and shaken well.
3. All observations are recorded.
II.) Bromine and sodium hydroxide
1. 5ml of dilute sodium hydroxide is poured into a clean test tube. A few drops of liquid bromine are added into this test tube.
2. The test tube is then closed with a stopper and shaken well.
3. All observations are recorded.
III.) Iodine and sodium hydroxide
1. 5ml of dilute sodium hydroxide is poured into a clean test tube. A small iodine crystal is added into this test tube.
3. All observations are recorded.
RESULTS
HALOGEN OBSERVATION
REACTION WITH WATER REATION WITH SODIUM HYDROXIDE
CHLORINE YELLOW TO BLUE BLUE
BROMINE NOT CHANGE BLUE
IODINE NOT CHANGE BLUE
DISCUSSIONS
i) Halogens react with water to form acid. For example :
Chlorine reacts with water to form hydrochloric acid and hypochlorous acid, a solution that can be used as a disinfectant or bleach:
Cl2 + H2O ->HCl + HClO
Bromine slowly reacts with water to form hydrogen bromide and hypobromous acid.
Br2 + H2O ->HBr + HBrO
Iodine reacts slightly with water to form hydrogen iodide and hypoiodous acid.
The reaction between iodine and water and between bromine and water does not give any changes to the pH paper because the reaction is too slow.
ii) Halogens react with sodium hydroxide to form salt and water.
Chlorine reacts with sodium hydroxide to form sodium chlorate and water. Cl2 + 2NaOH ->NaCl + NaOCl + H2O
Bromine reacts with sodium hydroxide to form sodium bromide and water. Br2 + 2NaOH ->NaBr + NaBrO +H2O
Iodine reacts with sodium hydroxide to form sodium iodide and water. 6NaOH + 3I2 ->5NaI + NaIO3 + 3H2O
QUESTIONS 1.
HALOGEN
REACTION WITH WATER REATION WITH SODIUM HYDROXIDE
CHLORINE Cl2 + H2O -> HCLO + HCl Cl2 + 2NaOH --- NaCl + NaOCl + H2O
BROMINE Br2 + H2O ->HBrO + HBr Br2 + 2NaOH = NaBr + NaBrO +H2O
IODINE I2 + H2O -> HIO + HI 3I2 + 6NaOH= 5NaI + NaIO3 + 3H2O
2. There are two properties of halogen other than those observed in this experiment . First, halogen have high effective nuclear charge, therefore they are highly electronegative. They gain an electron through reaction with other elements.
Next, halogens are highly reactive, and will combine directly with almost all elements. Due to this high level of reactivity, the halogens are almost never found in pure form; rather, they have to be extracted.
3. The reactivity of halogens based on the periodic table: The halogen elements have seven valence electrons,they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups. Halogens are one electron short in the outermost (p) shell, adding an electron creates a stable configuration, hence releases energy. The further you go up the halogen series (i.e. bromine->flourine) the closer the outer orbit is to the nucleus, hence the greater the attraction and hence the higher the electronegativity of the halogen.
PRECAUTIONS :
•Always ensure that you wear proper fitting clothes and nothing that is too loose. You should also wear your lab coat to avoid spilling anything on your clothes.
•Make sure you read the bottle labels carefully and only use what you are supposed to use during an experiment. You should not try out anything on your own unless you are very sure of what reagents or chemicals you need to use and their results
•Use rubber stopper to seal the mouth of the test tube.
•Make sure that the the test tube is in a clean and dry condition before using it.
•Place the eyes perpendicularly to the scale of graduated cylinder during the measuring of distilled water, sodium hydroxide, chlorine and bromine to avoid parallax error.
CONCLUSION :
When chlorine react with water , the pH paper turns from yellow to blue. There are no change when bromine and iodine react with water. When chlorine, bromine and iodine react with sodium hydroxide, pH paper turns from yellow to blue.
REFERENCES :
1. http://www.docbrown.info/page03/The_Halogens.htm
2. http://wiki.answers.com/Q/Reaction_of_halogen_with_water_and_sodium_hydroxide 3. http://wiki.answers.com/Q/What_is_the_Equation_for_chlorine_water
